1. Field of the Invention
The present invention relates to a dynamoelectric machine winding joining method, and particularly relates to a winding joining method applied to joining a stator winding for an alternator mounted to an automotive vehicle such as a passenger car or a truck.
2. Description of the Related Art
Conventionally, in the joining of dynamoelectric machine stator windings, a joining method is generally adopted in which an arc is discharged between an electrode and a winding joint portion and the heat thereof is used to fuse the winding together, as described in Japanese Patent Non-Examined Laid-Open No. 2000-350421, for example.
A conventional dynamoelectric machine winding joining method such as described in Japanese Patent Non-Examined Laid-Open No. 2000-350421, for example, will now be explained with reference to FIG. 19.
First, the construction of a stator to which this winding joining method is applied will be explained.
In this stator, U-shaped copper wires coated with an electrical insulator, for example, are inserted two by two into pairs of slots three slots apart such that return portions thereof are aligned at a first end surface of a stator core. In each of the pairs of slots, a first U-shaped copper wire is inserted into a first position and a second position from an inner circumferential side, and a second U-shaped copper wire is inserted into a third position and a fourth position from the inner circumferential side. In each of the slots, four copper wires are housed so as to line up in a single row in a radial direction.
At a second end surface of the stator core, free end sections of all of the U-shaped copper wires which are at an identical radial position are inclined in a like circumferential direction, and free end sections of radially-adjacent U-shaped copper wires are inclined in opposite circumferential directions. Then, the free ends 50 of each of the U-shaped copper wires are bent to face axially outward. In addition, the free ends 50 of the U-shaped copper wires projecting from the first position and the second position in each of the pairs of slots three slots apart are stacked in a radial direction, and the free ends of the U-shaped copper wires projecting from the third position and the fourth position in each of the pairs of slots three slots apart are stacked in a radial direction.
Thus, at the second end surface of the stator core, as shown in FIG. 19, the free ends 50 of the U-shaped copper wires form two pairs in a radial direction, and are arranged at a pitch of one slot in a circumferential direction. A clearance having a predetermined spacing is disposed between the two radially-adjacent pairs of free ends 50 for electrical insulation.
After the U-shaped copper wires constituting a stator winding are mounted to the stator core in this manner, an inner circumferential positive electrode 51 is disposed from the inner circumferential side of the stator core so as to contact the free ends 50 of the U-shaped copper wires positioned at an innermost circumference, an outer circumferential positive electrode 52 is disposed from an outer circumferential side of the stator core so as to contact the free ends 50 of the U-shaped copper wires positioned at the outermost circumference, and bar-shaped positive electrodes 53 are disposed so as to span between the inner and outer circumferential positive electrodes 51 and 52, the bar-shaped positive electrodes 53 being disposed between circumferentially-adjacent free ends 50 so as to contact circumferential side surfaces of each of the free ends 50.
Next, a torch 54 is moved above a pair of the free ends 50, a predetermined voltage is applied between the torch 54 and each of the electrodes 51, 52, and 53, and an inert gas, such as argon, helium, or the like, is supplied to the torch 54. Hence, an arc discharge 55 is generated between the torch 54 and the pair of free ends 50, fusing the pair of free ends 50 of the U-shaped copper wires together.
Each of the pairs of free ends 50 of the U-shaped copper wires are joined together sequentially by moving the torch 54 in a circumferential direction (or a radial direction). Thus, a stator winding is obtained which is composed of U-shaped copper wires linked into a desired pattern.
In the conventional dynamoelectric machine winding joining method, as explained above, the free ends 50 in each of the pairs are fused together by placing the inner and outer circumferential positive electrodes 51 and 52 on the innermost circumference and the outermost circumference of two pairs of free ends 50 arranged in single rows in a radial direction and inserting the bar-shaped positive electrodes 53 between the circumferentially-adjacent pairs of the free ends 50.
Thus, in the conventional winding joining method, if radial restraint of the free ends 50 on the innermost circumference by the inner circumferential positive electrode 51 is too small, the free ends 50 on the inner circumferential side are not placed in close contact with each other, making it necessary to melt the free ends 50 excessively. As a result, one problem has been that arc heat rises, giving rise to degradation of an electrically-insulating coating on the U-shaped copper wires, thereby making electrical insulation poor. In the worst cases, the free ends 50 on the inner circumferential side are too far apart from each other, and there has been a risk that they could not be joined together. If the radial restraint of the free ends 50 on the innermost circumference by the inner circumferential positive electrode 51 is too large, the free ends 50 are joined together with only a narrow radial clearance between the pairs of free ends 50. As a result, another problem has been that the joint portions may be short-circuited between the radially-adjacent pairs of free ends 50 by vibration or exposure to moisture, etc. Moreover, there are similar problems with the radial restraint of the free ends 50 on the outermost circumference by the outer circumferential positive electrode 52.
Because the radial clearance between the pairs of free ends 50 is very narrow compared to the clearance between circumferentially-adjacent the free ends 50 from the viewpoint of the construction of the stator core, it is extremely difficult to manage the radial restraint of the free ends 50 by the inner and outer circumferential positive electrodes 51 and 52, and in the worst cases, radially-adjacent pairs of the free ends 50 may be joined to each other erroneously. Thus, another problem has been that joining workability and yield have been poor.